Astrofísica, Cosmologia e Gravitação

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http://repositorio.ufes.br/handle/10/17488
Programa de Pós-Graduação em Astrofísica, Cosmologia e Gravitação

Centro: CCE
Telefone: (27) 4009 2488
URL do programa: https://cosmologia.ufes.br/pt-br/pos-graduacao/PPGCosmo

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Navegando Astrofísica, Cosmologia e Gravitação por Autor "Alcaniz, Jailson Souza de"

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    Quantum effects in cosmology
    (Universidade Federal do Espírito Santo, 2020-08-28) Frion, Emmanuel; Pinto Neto, Nelson; https://orcid.org/0000-0001-6713-5290; http://lattes.cnpq.br/6196081550581346; https://orcid.org/0000000312800315; Fabris, Julio Cesar; https://orcid.org/000000018880107X; http://lattes.cnpq.br/5193649615872035; Rodrigues, Davi Cabral; https://orcid.org/0000000316835443; http://lattes.cnpq.br/5465449494182034; Bergliaffa, Santiago Esteban Perez; Alcaniz, Jailson Souza de; Peter, Patrick; Wands, David Graham
    Even though predictions from inflationary models fit observations with great accuracy, inflation is not a theory, and it is therefore important to look at alternative mechanisms whose phenomenology can be constrained by cosmological data. It is possible to explain the origin of large-scale structures through bouncing models, taking into account the evolution of quantum perturbations in both a contracting phase and an expansion phase. This thesis is motivated by the effects of quantum perturbations on cosmological models. We first focus on a semi-classical description of quantum perturbations in the form of stochastic noise in a collapsing universe. The growth of perturbations is a fundamental issue in bouncing cosmologies that any acceptable model must treat accurately. To this end, we quantified how quantum perturbations may overcome the classical energy density in the simple case of a massless field with exponential potential. This is generally not the case within this configuration, although there is an important growth of quantum diffusion in the case of a matter-dominated model, which could possibly drive the system away from the classical evolution. This stochastic collapse is the first step towards a complete stochastic bouncing model. Numerous non-singular bouncing models resolve the initial singularity issue thanks to quantum effects. They constitute a broad class of relevant cosmological models, since they solve many problems of standard inflation. A subclass is obtained by considering the canonical quantisation of general relativity using the de Broglie-Bohm interpretation of quantum mechanics. In the second part of the thesis, we show that the generation of magnetic fields in such models compatible with observations on cosmological scales can be obtained with a simple coupling between gravity and electromagnetism. Interestingly, bouncing magnetogenesis have intrinsically less issues than inflationary magnetogenesis. The model presented here shows that acceptable magnetic fields can be obtained, depending on the energy scale of the coupling and the time when the bounce occurs. To close the thesis, we finish with a bouncing model obtained from the affine quantisation of the Brans-Dicke theory. Contrary to canonical quantisation, the affine procedure needs less assumptions and kinetic energy terms possess a quantum potential regularising the dynamics, resulting in a smooth bounce. Another advantage of this method lies in the choice of mathematical models one can use to tackle the same physical problem. We employ this asset to deal with the quantum equivalence of Jordan and Einstein frames, an issue of modified gravity models. The results point toward an unitary equivalence of the frames. We conclude with a summary of achievements.
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    Weak gravitational lensing in interacting dark sector models
    (Universidade Federal do Espírito Santo, 2025-08-22) Capel Sica, Paola Terezinha Zanolla Seidel e; Silva, Saulo Carneiro de Souza; https://orcid.org/0000-0001-7098-383X; http://lattes.cnpq.br/; Benetti, Micol; https://orcid.org/0000-0002-3670-7214; http://lattes.cnpq.br/3234425698221975; Fabris, Júlio César; https://orcid.org/0000-0001-8880-107X; http://lattes.cnpq.br/5193649615872035; https://orcid.org/0000-0002-5403-8923; http://lattes.cnpq.br/; Alcaniz, Jailson Souza de; https://orcid.org/0000-0003-2441-1413; http://lattes.cnpq.br/4351190607357917; Velten, Hermano Endlich Schneider; https://orcid.org/0000-0002-5155-7998; http://lattes.cnpq.br/0282590467459210; von Marttens, Rodrigo Fernando Lugon Cornejo; https://orcid.org/0000-0003-3954-5756; http://lattes.cnpq.br/7980376506204515; Marques, Gabriela Antunes; https://orcid.org/0000-0002-8571-8876; http://lattes.cnpq.br/0675863411047105
    We explore the lines that underpin the knowledge of weak gravitational lensing, study ing basic cosmological concepts, and the construction of the matter power spectrum for ΛCDM and different scenarios. Our main goal is to investigate the possibility of interaction in the dark sector through a set of models that employ the weak lens ing formalism. This strategy proves to be promising, as the three-dimensional matter power spectrum can be directly probed with this tool. Another objective is to update the constraints on relevant cosmological parameters, including the interaction param eter of the proposed model. The spacetime is assumed to be flat and described by the Friedmann–Lemaˆıtre–Robertson–Walker metric, applied to a non-adiabatic decom posed generalized Chaplygin gas. In this framework, we recover the behavior of cold dark matter at high redshifts and of a cosmological constant in the asymptotic limit. Numerical testing is therefore crucial to evaluate the models. For this purpose, we use the CLASS Boltzmann code to simulate the interaction model, and the Cobaya sampler to compare different models, particularly with cosmic shear data from the first year of the DES-Y1 survey and with CMB data. We know that early and late-time observables do not agree with the theme of dark sector dynamics, and in this context, our investigation may contribute to assessing whether a systematic discrepancy exists between these measurements. In general, our results are consistent with the CMB data, except for the Hubble constant, H0. Our best-fit value for this parameter was lower than the standard CMB value. We find that, in the context of this dark sector study, the interaction is strongly constrained and the ΛCDM model is favored.